Devices made in silicon have been mounted directly onto printed circuit boards for many years. The problem is that the back surface of the device can still be electrically active, which can lead to corrosion and increased temperatures on the back surface. If a heat sink is used for cooling, insulation is often needed on the back surface of the device, which increases device size and cost.
FIG. 1 shows an example of a known device 1 surface mounted onto a printed circuit board 17. The printed circuit board 17 has copper traces 15. Solder bumps 14, separated by polyimide passivation 16, electrically and physically couple the active area 13 of the device to the copper traces 15 on the printed circuit board 17. Device 1 has a sidewall 12 and a back surface 11. Sidewall 12 and back surface 11 are electrically connected to the circuit on the front side.
FIG. 2 shows a heat sink 19 attached to device 1 to conduct heat away from the back surface 11 of the silicon substrate 10. When a heat sink 19 is attached to the back surface 11 of device 1, insulation 18 must be added between the silicon substrate 10 and the heat sink 19 to prevent the heat sink 19 from becoming electrically active through contact with back surface 11 that is electrically connected to the front side. However, the addition of insulation 18 disadvantageously impedes the ability of the heat sink 19 to conduct heat away from the device 1.
Accordingly, a solution to the above-noted problem is needed, namely a device in which the heat sink can be directly connected to the back surface of a surface mounted device without the need for an insulation layer that impedes the passage of heat from the device.